The application incorporates by reference the subject matter of Application No. 2002-151361 filed in Japan on May 25, 2002, on which a priority claim is based under 35 U.S.C. xc2xa7 119(a).
1. Field of the Invention
The present invention relates to a valve system for an internal combustion engine capable of opening and closing intake valves and exhaust valves of the internal combustion engine at different timings.
2. Description of the Related Art
In recent years, a valve system (also referred to as xe2x80x9cvariable valve systemxe2x80x9d), which is capable of changing operating characteristics (such as opening/closing timing, opening time, and so forth) of intake valves and exhaust valves (hereinafter generically referred to as xe2x80x9cengine valvesxe2x80x9d or xe2x80x9cvalvesxe2x80x9d) provided in a reciprocating internal combustion engine (hereinafter referred to as xe2x80x9cenginexe2x80x9d) to the optimum characteristics according to engine load and speed, have been developed and put into practical use.
As an example of a mechanism for changing operating characteristics as described above, a variable valve system is disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2001-41017. This variable valve system is comprised of a connection mechanism constructed such that a low-speed rocker arm is provided with a hydraulic piston, and an engagement projection formed in a high-speed rocker arm is selectively engaged with the piston such that the valve timing can be switched between a low speed and a high speed. Further, this variable valve system is comprised of return springs that inhibit the rocker arms from getting away from respective corresponding cams.
It is therefore an object of the present invention to provide a valve system for an internal combustion engine, which has a connection mechanism pressed against a cam by force other than return springs of engine valves.
To attain the above object, the present invention provides a valve system for an internal combustion engine, comprising: a first rocker arm supported by a first rocker shaft such that it rocks when driven by a first cam, and having an end thereof connected to one of an intake valve and an exhaust valve; a second rocker arm supported by the first rocker shaft such that the second rocker arm rocks when driven by a second cam having a different cam profile from that of the first cam, the second rocker arm being disposed adjacent to the first rocker arm; and a connection switching mechanism that switches the state of the first rocker arm between a state in which the first rocker arm is connected to the second rocker arm and a state in which the first rocker arm is disconnected from the second rocker arm. As a result, when the connection switching mechanism is brought into the state in which the first rocker arm and the second rocker arm are connected, the first rocker arm rocks integrally with the second rocker arm to open and close one of the intake valve and the exhaust valve according to the cam profile of the second cam, and when the connection switching mechanism is brought into the state in which the first rocker arm is disconnected from the second rocker arm, the first rocker arm rocks without being affected by the movement of the second rocker arm to open and close one of the intake valve and the exhaust valve according to the cam profile of the first cam.
Further, the valve system for the internal combustion engine comprises a forcing member that forces the second rocker arm toward the second cam while the second rocker arm is rocking so as to follow the rotation of the second cam. The second rocker arm can rock according to the cam profile of the second cam while being abutted against the second cam in a reliable manner. A support member that supports the forcing member is rotatably supported by a support shaft provided on a cylinder head, and is configured such that a locking structure inhibits the forcing member from rotating about the support shaft, so that the forcing member can support the forcing member in a reliable manner.